Development of a novel class of peroxisome proliferator-activated receptor (PPAR) gamma ligands as an anticancer agent with a unique binding mode based on a non-thiazolidinedione scaffold.

We previously identified dibenzooxepine derivative 1 as a potent PPARγ ligand with a unique binding mode owing to its non-thiazolidinedione scaffold. However, while 1 showed remarkably potent MKN-45 gastric cancer cell aggregation activity, an indicator of cancer differentiation-inducing activity induced by PPARγ activation, we recognized that 1 was metabolically unstable. In the present study, we identified a metabolically soft spot, and successfully discovered 3-fluoro dibenzooxepine derivative 9 with better metabolic stability. Further optimization provided imidazo[1,2-a]pyridine derivative 17, which showed potent MKN-45 gastric cancer cell aggregation activity and excellent PK profiles compared with 9. Compound 17 exerted a growth inhibitory effect on AsPC-1/AG1 pancreatic tumor in mice. Furthermore, the decrease in the hematocrit (an indicator of localized edema, a serious adverse effect of PPARγ ligands) was tolerable even with oral administration at 200 mg/kg in healthy mice.

Development of Dihydrodibenzooxepine Peroxisome Proliferator-Activated Receptor (PPAR) Gamma Ligands of a Novel Binding Mode as Anticancer Agents: Effective Mimicry of Chiral Structures by Olefinic E/ Z-Isomers.

A novel class of PPARγ ligand 1 (EC50 = 197 nM) with a dibenzoazepin scaffold was identified through high-throughput screening campaign. To avoid the synthetically troublesome chiral center of 1, its conformational analysis using the MacroModel was conducted, focusing on conformational flip of the tricyclic ring and the conformational restriction by the methyl group at the chiral center. On the basis of this analysis, scaffold hopping of dibenzoazepine into dibenzo[ b, e]oxepine by replacing the chiral structures with the corresponding olefinic E/ Z isomers was performed. Consequently, dibenzo[ b, e]oxepine scaffold 9 was developed showing extremely potent PPARγ reporter activity (EC50 = 2.4 nM, efficacy = 9.5%) as well as differentiation-inducing activity against a gastric cancer cell line MKN-45 that was more potent than any other well-known PPARγ agonists in vitro (94% at 30 nM). The X-ray crystal structure analysis of 9 complexed with PPARγ showed that it had a unique binding mode to PPARγ ligand-binding domain that differed from that of any other PPARγ agonists identified thus far.

Glucose concentration-dependent potentiation of insulin secretion by a new chemical entity, KCP256.

The insulinotropic activity of KCP256 [(R)-8-benzyl-2-cyclopentyl-7, 8-dihydro-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one hydrochloride] was examined using MIN6 cells (a pancreatic beta-cell line) and pancreatic islets isolated from rats. Unlike sulfonylurea anti-diabetic drugs, KCP256 dose-dependently (0.1-10 microM) enhanced insulin secretion from MIN6 cells and its insulinotropic effect was exerted only at high concentrations of glucose (8.3-22 mM) but not at low concentrations of glucose (3.3-5.5 mM). Furthermore, the action mechanism of KCP256 was different because, unlike sulfonylurea drugs, KCP256 did not displace the binding of [3H]glibenclamide, and did not inhibit the 86Rb+ efflux nor K(ATP) channel activity. In isolated islets, KCP256 also enhanced insulin secretion in a dose- and a glucose-concentration-dependent manner. Plasma levels of insulin after glucose challenge in KCP256-administrated rats were higher than those in vehicle-administrated animals, indicating that KCP256 can enhance insulin secretion in vivo. Since the insulinotropic activity of KCP256 only occurs at high concentrations of glucose, this novel drug may exhibit a decreased risk of drug-induced hypoglycemia compared with sulfonylurea drugs when treating patients with diabetes.

Inhibitory effect of the 4-aminotetrahydroquinoline derivatives, selective chemoattractant receptor-homologous molecule expressed on T helper 2 cell antagonists, on eosinophil migration induced by prostaglandin D2.

Prostaglandin (PG) D2, a major cyclooxygenase metabolite generated from immunologically stimulated mast cells, is known to induce activation and chemotaxis in eosinophils, basophils, and T helper 2 (Th2) lymphocytes via a newly identified PGD2 receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). CRTH2 is hypothesized to play an important role in the outcome of allergic responses. However, the absence of selective CRTH2 antagonists has prevented the elucidation of the role of CRTH2 in pathogenesis of allergic diseases. We now report compounds discovered as selective CRTH2 antagonists, (2R*,4S*)-N-(1-benzoyl-2-methyl-1,2,3,4-tetrahydroquinolin-4-yl)-N-phenylisobutyramide (K117) and (2R*,4S*)-N-(1-benzoyl-2-methyl-1,2,3,4-tetrahydroquinolin-4-yl)-N-phenylcyclopropanecarboxamide (K604). K117 and K604 have inhibitory effects on human CRTH2 with Ki values of 5.5 and 11 nM, respectively. The effect of these compounds is CRTH2-specific with no cross-reactivity against 15 other receptors and four arachidonic acid-metabolizing enzymes. K117 and K604 has no effect on the basal Ca2+ level and inhibited the Ca2+ response induced by PGD2 in 293EBNA cells expressing human CRTH2. Also, K117 and K604 inhibit PGD2-induced human eosinophil chemotaxis with IC50 values of 7.8 and 42.2 nM, respectively, but they do not inhibit the CC-chemokine receptor 3 agonist eotaxin-induced chemotaxis. These results indicate that K117 and K604 are highly potent and selective antagonists for human CRTH2. These compounds have possibilities to become useful tools to explore CRTH2 functions in allergic diseases.

Involvement of the active metabolites in the inhibitory activity of K579 on rat plasma dipeptidyl peptidase IV.

K579 ((S)-1-[4-methyl-1-(2-pyrimidinyl)-4-piperidylamino]acetyl-2-pyrrolidinecarbonitrile), which is a long-acting and a slow binding dipeptidyl peptidase IV inhibitor, preserved the endogenously secreted active forms of glucagon-like peptide-1, augmented the insulin response and ameliorated the glucose excursion during oral glucose tolerance test in rats. In this study, we measured plasma concentrations of K579 after oral administration to rats. However, K579 was eliminated rapidly from plasma after oral administration to rats. Therefore, we postulated that there are active metabolites of K579 in rat plasma. We investigated the effect of K579 on plasma dipeptidyl peptidase IV activity using bile duct-cannulated rats. The duration of inhibitory action of plasma dipeptidyl peptidase IV after the administration of K579 in bile duct-cannulated rats was shorter than that in sham-operated rats. Moreover, we investigated the effect of bile obtained from K579-treated rat on plasma dipeptidyl peptidase IV activity in normal rats. The bile collected from K579-treated rats exhibited tardive and potent inhibitory activity of normal rat plasma. These results suggest that K579 sustained the duration of inhibitory action of plasma dipeptidyl peptidase IV by the character as a slow-binding inhibitor and, as well, by the presence of metabolites of K579, which exhibit the inhibitory activity of dipeptidyl peptidase IV.

Effects of combination treatment with dipeptidyl peptidase IV inhibitor and sulfonylurea on glucose levels in rats.

The effects of orally administered dipeptidyl peptidase IV (DPP-IV) inhibitor on the glucose-lowering effect of glibenclamide are still unknown. We evaluated the effects of combination treatment with a long-lasting DPP-IV inhibitor, K579 ((S)-1-[4-methyl-1-(2-pyrimidinyl)-4-piperidylamino]acetyl-2-pyrrolidinecarbonitrile), and glibenclamide on the glycemic responses to glucose loading in rats. Treatment with K579 inhibited the plasma DPP-IV activity even 8 h after the administration. K579 significantly suppressed the blood glucose elevation in glibenclamide-pretreated rats without excessive hypoglycemia. These profiles of K579 indicate that it could be useful agent to correct the postprandial glucose excursion in type 2 diabetes patients by combination treatment with glibenclamide.

K579, a slow-binding inhibitor of dipeptidyl peptidase IV, is a long-acting hypoglycemic agent.

Dipeptidyl peptidase IV inhibitors are expected to be categorized in a new type of antidiabetic drugs. We had developed a long-acting dipeptidyl peptidase IV inhibitor, K579 [(S)-1-[4-methyl-1-(2-pyrimidinyl)-4-piperidylamino]acetyl-2-pyrrolidinecarbonitrile]. The aim of present study was to characterize the pharmacological profiles of K579. In normal rats, K579 suppressed the blood glucose elevation after an oral glucose tolerance test with the increment of plasma insulin and active forms of glucagon-like peptide-1 (GLP-1). During repetitive glucose loading using Zucker fatty rats, pretreatment with K579 attenuated the glucose excursion after the second glucose loading as well as the first glucose loading without inducing hypoglycemia. The kinetic study using cell extract revealed that K579 was a more potent and slower binding inhibitor than the existing dipeptidyl peptidase IV inhibitor (NVP-DPP728, 1-[[[2-[(5-cyanopyridin-2-yl)amino]ethyl]amino]acetyl]-2-cyano-(S)-pyrrolidine). These profiles of K579 might be advantageous over the existing dipeptidyl peptidase IV inhibitor with respect to less dosing frequency.